Simple fatty acid alkyl esters produced from fats and oils are being investigated in numerous settings as replacements for petroleum-derived materials, particularly diesel fuel. This invention relates to the production of fatty acid alkyl esters by a novel process. The process uses inexpensive reagents and simple technologies to quickly and efficiently produce fatty acid esters. The process involves (a) saponifying a feedstock (e.g., soy soapstock) with an alkali to form a saponified feedstock, (b) removing the water from the saponified feedstock to form a dried saponified feedstock containing no more than about 10% water, (c) esterifying the dried saponified feedstock with an alcohol by acid catalysis to form fatty acid alkyl esters, and (d) recovering the fatty acid alkyl esters. The process unexpectedly avoids elevated temperatures and pressures and incomplete esterification of all fatty acids in the starting material, and relatively long incubation times of known processes.
There is continued and growing interest in the use of renewable resources as feedstocks for replacements of petroleum-derived chemicals. It has long been known that diesel engines can use the triglycerides in fats and oils as fuels. However, their use eventually results in engine failure. This problem is alleviated by conversion of the fatty acids found in natural lipids into their simple esters, usually methyl or ethyl esters. An increasing body of evidence indicates that these esters perform well in essentially unmodified diesel engines and that, relative to petroleum-diesel fuel, they can reduce the output of particulate and hydrocarbon pollutants. The term biodiesel is applied to these esters, which are also being explored as replacements for nonrenewable chemicals in other applications, including cleaning agents, fuel additives, and substitutes for organic solvents.
Refined triglyceride oils have been the predominant feedstocks for the synthesis of biodiesel to date. However, such triglycerides are relatively high in cost, and result in a product that cannot compete economically with petroleum-derived diesel fuel. This has fostered investigation of the use of lower-value lipids, primarily animal fats and waste greases, as feedstocks. Soapstock, a lipid-rich byproduct of vegetable oil refining, is another relatively inexpensive source of fatty acids. It contains substantial amounts of glycerides, phosphoglycerides, and free fatty acids, the latter as their sodium, or less commonly potassium, salts. From soybeans, the predominant source of edible oil in the United States, soapstock is generated at a rate of about 6% of the volume of crude oil produced, amounting to as much as nearly one billion pounds of soapstock annually. Compared to refined oils, soapstock represents an inexpensive source of fatty acids since its price can be as low as one-tenth that of refined vegetable oil.
While there are several possible feedstocks for biodiesel production, it is notable that, relative to the use of e.g. waste grease as a feedstock, soapstock is a potentially attractive source of simple fatty acid esters. This is because (a) its production is relatively centralized, eliminating the need for a collection infrastructure, and (b) soapstock is not routinely subjected to the potentially damaging, extended, repeated high temperature regimes typical of waste greases.
Some methods for the production of fatty acid methyl esters (FAME) from soapstock have been reported (Stern, R., et al., Preparation of Methyl and Ethyl Esters from Crude Vegetable Oils and Soapstock, Proceedings: World Conference on Emerging Technologies in the Fats and Oils Industry, edited by A. R. Baldwin, American Oil Chemists"" Society, Champaign, 1986, pp. 420-422; Sonntag, N. O. V., Fat Splitting, Esterification, and Interesterification, in Bailey""s Industrial Oil and Fat Products, edited by D. Swern, Vol. 2, 4th edn, J. Wiley and Sons, New York, 1982, pp. 97-173; Haas, M. J., and K. M. Scott, J. Am. Oil Chem. Soc., 73: 1393-1401 (1996)). For example, one commerical process employs various feedstocks (e.g., soapstock-derived acid oils with free fatty acid levels up to 60%) to synthesize fatty acid esters by esterifying the feedstocks in the presence of methanol or ethanol for 10-12 hours at temperatures of 100xc2x0-120xc2x0 C. (which implies the use of a pressurized system). In addition, U.S. Pat. No. 5,525,126 discloses production of fatty acid esters from soapstock by utilizing barium and calcium acetates as catalysts at temperatures of 200xc2x0-220xc2x0 C. for 1-3 hours in a pressurized system. Furthermore, Formo (J. Am. Oil Chem. Soc., 31:548-559 (1954)) disclosed that several hours reflux are required to obtain high degrees of esterification of free fatty acids. However, the prior art methods have disadvantages which include their use of elevated temperatures and pressures, incomplete esterification of all fatty acids in the starting material, and/or relatively long incubation times.
There have apparently been no reports of using inexpensive reagents and simple technologies to quickly and efficiently produce fatty acid esters from feedstocks such as soapstock, both to address the economic challenges facing biodiesel and to provide new routes for soapstock utilization. The process of the present invention unexpectedly avoids elevated temperatures and pressures, incomplete esterification of all fatty acids in the starting material, the need to eliminate all water from the reaction mixture, and the relatively long incubation times of the prior art.
We have discovered a method for producing fatty acid alkyl esters from a feedstock, involving:
(a) saponifying the feedstock with an alkali to form a saponified feedstock,
(b) removing the water from the saponified feedstock to form a dried saponified feedstock containing no more than about 10% water,
(c) esterifying the dried saponified feedstock with an alcohol and an inorganic acid catalyst to form fatty acid alkyl esters (even when the reaction mixture contains up to about 3% water), and
(d) recovering the fatty acid alkyl esters.